Construction of oxygen-rich vacancy Bi3O4Br:Yb3+,Er3+ nanosheets for enhanced photoreversible color switching and upconversion luminescence

Traditional inorganic photoreversible color-switching materials (PCSMs) usually exhibit slow color switching and single color switching characteristics, which severely restrict their use in information storage, anti-counterfeiting, and other applications. Herein, we report a fast photoresponsive color-switching inorganic PCSM based on oxygen-vacancy (OV) Bi3O4Br:Yb3+,Er3+ (BYE-OV) nanosheets. The BYE-OV nanosheets demonstrated considerable photoreduction activity and effective charge carrier separation when exposed to ultraviolet (UV) light, resulting in a rapid change in color from light yellow to dark brown. Moreover, under 980-nm excitation, the green and red emissions of the BYE-OV nanosheets were considerably enhanced, being 9.6 and 8.8 times higher than those of the BYE nanosheets, respectively. Additionally, BYE-OV nanosheets were combined with an agarose hydrogel to produce BYE-OV/agarose nanocomposite films, which exhibited excellent photoreversible color switching and upconversion (UC) luminescence. This research provides new insights into the development of innovative inorganic PCSMs, thereby considerably broadening their potential applications.